Performance and sync rep
Sync rep allows us to offer a confirmation to the user that a transaction has been committed and fully replicated on at least one standby server. To do that, we must wait for the transaction changes to be sent to at least one standby, and then have that feedback returned to the primary.
The additional time taken for the message's round trip will add elapsed time for the commit of write transactions, which increases in proportion to the distance between servers. PostgreSQL offers a choice to the user as to what balance they would like between durability and response time.
Getting ready
The user application must be connected to a primary to issue transactions that write data. The default level of durability is defined by the synchronous_commit parameter. That parameter is user-settable, so it can be set for different applications, sessions, or even individual transactions. For now, ensure that the user application is using this level:
